Disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and embedded servo sectors. The embedded servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo controller to control the velocity of the actuator arm as it seeks from track to track.
FIG. 1 shows a prior art disk format 2 as comprising a number of servo tracks 4 defined by servo sectors 60-6N recorded around the circumference of each servo track. Each servo sector 6i comprises a preamble 8 for storing a periodic pattern, which allows proper gain adjustment and timing synchronization of the read signal, and a sync mark 10 for storing a special pattern used to symbol synchronize to a servo data field 12. The servo data field 12 stores coarse head positioning information, such as a servo track address, used to position the head over a target data track during a seek operation. Each servo sector 6, further comprises groups of servo bursts 14, which are recorded with precise intervals and offsets relative to the track centerlines. The servo bursts 14 provide fine head position information used for centerline tracking while accessing a data track during write/read operations.
There are several prior art techniques for writing the servo sectors to the disk, including an external servo writer that writes the servo sectors by controlling the head internal to the disk drive using precise external positioning mechanics, such as a laser interferometer. Other techniques may involve self servo writing the servo sectors by servoing off of a seed pattern, or by propagating the servo sectors across the radius of the disk. In yet another technique, a media writer may simultaneously write the servo sectors to a number of disk surfaces, and then one or more of the servo written disks installed into a production disk drive. A similar technique may use a printing technique (e.g., stamping or etching technique) to servo write the disks which are then inserted into a production disk drive.